As a multiplexing hierarchy of an optical communication network that can transfer a client signal over a long distance with a large capacity, OTN (Optical Transport Network) was recommended as a standardized technique in G.709 by ITU-T in 2001 (refer to non-patent document 1). The OTN has strong management and monitoring functions, and realizes transmission of large capacity by introducing error correction code into the frame format. In the conventional OTN, multiplexing hierarchies for accommodating SDH/SONET (Synchronous Digital Hierarchy/Synchronous Optical Network) and Ethernet are defined. But, types of client signals accommodated by the OTN are diversified with development of ICT (Information and Communication Technology) and with spread and expansion of multimedia services, thus, new multiplexing hierarchies for efficiently accommodating such diversified client signals are additionally defined in G.709 ver. 3 in 2009 (refer to non-patent document 1).
In the conventional OTN, three bit rates of ODU1 (Optical channel Data Unit 1: 239/238×2488320 kbit/s), ODU2 (239/237×9953280 kbit/s), and ODU3 (239/236×39813120 kbit/s) are defined. On the other hand, in OTN in G.709 ver.3, ODU0 (1244160 kbit/s), ODU2e (239/237×10312500 kbit/s), ODU4 (239/227×99532800 kbit/s), and ODUflex are newly added, in which, for ODUflex, the bit rate is 239/238× client signal bit rate in a case where the client signal is a CBR signal and is mapped to ODUflex, and refer to tables 7-8 of the non-patent document 1 for the bit rate in a case where the client signal is encapsulated by GFP-F and mapped to ODUflex. Thus, it becomes possible to provide payload capacities according to bit rates of various client signals.
Also, as mapping schemes, GMP (Generic Mapping Procedure) is newly defined in addition to AMP (Asynchronous Mapping Procedure) and BMP (Bit-synchronous Mapping Procedure). GMP is a mapping method by which a mapping position of a client signal can be determined from the bit rate of the client signal and a payload capacity of an OTN frame that accommodates the client signal.
As mentioned above, thanks to introduction of the newly added ODUs and the GMP scheme, diversified client signals can be accommodated in OTN flexibly and efficiently, so that it is considered that transceivers using OTN will become widespread.
Although various client signals can be accommodated, when accommodating a client signal such as a video signal for which jitter regulation is strict in OTN, there is a fear that destuff jitter may affect transmission quality of the client signal. For accommodating or multiplexing client signals in OTN asynchronously, stuff processing is performed for absorbing frequency deviation. But, since the phase of the reading clock varies when removing a stuff byte at a receiving end, destuff jitter occurs. The destuff jitter occurs according to an inserting cycle of the stuff byte. Thus, if the cycle for inserting the stuff byte is extremely long, destuff jitter of low frequency component occurs, so that it becomes difficult to suppress the destuff jitter by PLL (Phase Locked Loop) and the like.
As a technique for suppressing destuff jitter, there is a method for putting restrictions on clock frequencies such that an area of frequency deviation where a stuff insertion ratio is extremely small is not used (refer to patent document 1).
Also, there is a method for inserting a stuff of 1 bit in a distributed manner for each parallel processing when accommodating a low order frame to a high order frame (refer to patent document 2).